1. Field of the Invention
The present invention relates to various types of printers, paper conveying apparatuses which are provided in image reading apparatuses and the like, printing apparatuses using the same, more particularly, to paper conveying apparatuses and printing apparatuses capable of conveying paper without troublesome problems.
2. Description of the Related Art
In a paper conveying apparatus which is provided in printers of various types, etc., it is necessary to prevent occurrence of printing irregularities resulting from variation in the conveyance status of paper. In order to achieve and maintain satisfactory paper conveyance (sub-scanning operation) over the entire recording region, a variety of constructions have been proposed to date.
Taken up as one example is a recording apparatus disclosed in Japanese Unexamined Patent Publication JP-A 5-69610 (1993). In this recording apparatus, to eliminate adverse effects of backlash occurring in the driving system for conveying recording paper and to enable to achieve a satisfactory sub-scanning operation over the entire recording region, a first conveying roller and a second conveying roller are arranged on upstream and downstream sides of a recording position along a direction in which paper is conveyed (paper conveying direction). The first and second conveying rollers are driven by a single, common motor. The second conveying roller is set to be greater in conveying speed than the first conveying roller. The first conveying roller is so designed as to convey paper at a lower than normal speed over a certain period of time during a tail end of recording paper passes through the first conveying roller.
Taken up as another example is an ink-jet recording apparatus disclosed in Japanese Unexamined Patent Publication JP-A 8-208094 (1996). This ink-jet recording apparatus is simple in structure and requires low manufacturing cost. In this construction, recording paper under discharge is kept from contact with a recording face of already discharged paper by curling the middle part of the paper under discharge. After the completion of the discharge, the paper is superimposed upon the already discharged paper under its own weight. In order to prevent occurrence of a smear resulting from a rub against the recording surface, a plurality of spurs, which are brought into press-contact with a paper discharge roller, are arranged in such a way that the ones located closer to both ends are selectively positioned forward along a paper feeding direction, or the spurs are arranged only at end portions in the direction of paper width, and in the vicinity of the paper discharge roller is disposed a paper guide for lifting a central portion in the direction of paper width of the recording paper. Thereby, the central portion in the direction of paper width of the recording paper is kept in a suspended state during the discharge.
Taken up as still another example is a recording apparatus disclosed in Japanese Unexamined Patent Publication JP-A 10-297039 (1998), which is devised with the aim of providing a recording apparatus incorporating paper discharge means in which spurs can be disposed at high density without additionally providing a paper discharge roller shaft. In this construction, spurs are located face to face with a paper discharge roller in a direction such as to sandwich a material to be recorded, and the spurs are alternately disposed at two different parallel shaft positions, thereby constituting a first spur group and a second spur group. An interval L2 between the adjacent spurs of the first and second spur groups is set to be shorter than a length L1 of an elastic shaft of the spur.
In the ink-jet recording apparatus, its paper conveying apparatus is generally constructed as follows. On upstream and downstream sides of a printing section for performing printing are arranged first conveying means and second conveying means, respectively. Paper is fed to the printing section by the first conveying means, and, after undergoing printing, the paper is conveyed along a paper discharge direction by the second conveying means. In this construction, however, undesirable printing irregularities occur frequently. Details are given below.
That is, at the time when the just-printed paper reaches the second conveying means, a leading end of the paper abuts against the second conveying means. At the instant when the paper is get caught in the roller, resistance is increased, and the paper is abruptly put under heavy load. Resultantly, the paper is subjected to a force in a direction in which its movement comes to halt. This causes variation in the amount of paper conveyance, resulting in printing irregularities. Such a detrimental effect attributed to variation in the amount of paper conveyance may appear not only in the ink-jet recording apparatus but also in other like apparatuses. For example, in an image reading apparatus, as a result of variation in the amount of paper conveyance, the paper conveying direction is disturbed, resulting in an readout image being misregistered.
However, the aforementioned constructions each have drawbacks. Firstly, in the recording apparatus disclosed in JP-A 5-69610, the second conveying means, disposed on the downstream side of the printing head, is composed of the second conveying roller and a second driven roller. The second driven roller is simply retained by a second holding member and is kept press-contact with the second conveying roller by a second spring. That is, this construction pays no regard to measures for reducing variation in a load imposed on paper. Thus, there is a possibility that printing irregularities occur due to the variation of the paper conveying direction as described above.
Secondly, in the ink-jet recording apparatus disclosed in JP-A 8-208094, a plurality of spurs, which are brought into press-contact with the paper discharge roller, are arranged in such a way that the ones located closer to both ends are selectively positioned forward along the paper feeding direction, or the spurs are arranged only at the end portions in the direction of paper width, and in the vicinity of the paper discharge roller is disposed the paper guide for lifting the widthwise central portion of the recording paper. In this case, a plurality of spurs are arranged in different positions solely for the purpose of subjecting paper to curling. That is, this construction pays no regard to measures for adjusting a load imposed on paper.
Thirdly, in the recording apparatus disclosed in JP-A 10-297039, a plurality of spurs are alternately disposed at two different parallel shaft positions for the purpose of preventing a rippling phenomenon (so-called cockling) that appears in a direction perpendicular to the paper conveying direction. This allows the spurs to be disposed at high density without additionally providing a paper discharge roller shaft. In this case, however, a larger number of constituent components are required, resulting in the manufacturing cost being increased. This construction also pays no regard to measures for adjusting variation in a load imposed on paper.